Titanium esters react with high molecular weight hydroxyl-containing compounds so as to cross-link them and produce gels; J. Oil and Colour Chem. Assoc. 31, 405 (1948). However, simple alkyl titanates effect the cross-linking reaction at a rate that is too rapid for most industrial uses. The cross-linking reaction rate can be depressed by combining a titanium ester with a variety of multifunctional compounds. Examples of multifunctional compounds which have been reacted with simple alkyl esters of titanium include an .alpha.-hydroxycarboxylic acid in U.S. Pat. No. 2,870,181; 2,4-pentanedione or an acetoacetate in U.S. Pat. No. 2,680,108; and a1kanolamines, such as triethanolamine, in U.S. Pat. No. 2,950,174 and 3,301,733.
Russell, in U.S. Pat. No. 2,898,356, disclosed that chelated titanium salts of .alpha.-hydroxy acids may be useful in the textile, leather and cosmetic industries, but that they may not be used at an alkaline pH. He proposed, therefore, a method for the preparation of a stabilized solution of such salts in alkaline aqueous media which comprises admixing a chelated titanium salt of an .alpha.-hydroxy acid with a polyol. He disclosed also that the chelated titanium salt of the .alpha.-hydroxy acid may be prepared by reacting an alkyl ester of ortho-titanic acid with an .alpha.-hydroxy acid or by reacting a titanium salt of an inorganic acid with an .alpha.-hydroxy acid. In the examples involving an inorganic titanium salt, Russell formed an aqueous solution of titanium tetrachloride or titanyl sulfate with sorbitol and then added malic or citric acid to it.
My U.S. Pat. No. 4,609,479 discloses and claims a process which comprises combining (i) a polyol selected from glycerol, erythritol, arabitol, xylitol, sorbitol, dulcitol, mannitol, inositol, monosaccharides, and disaccharides, (ii) water and (iii) an .alpha.-hydroxy carboxylic acid selected from lactic acid, glycolic acid, malic acid, citric acid, tartaric acid, saccharic acid, gluconic acid, glyceric acid and mandelic acid, and then reacting that combination of materials with a tetravalent titanium compound of an inorganic acid at an .alpha.-hydroxy carboxylic acid titanium mol ratio between about 1:1 and about 3:1 and a polyol:titanium mol ratio between about 0.25:1 and about 2:1.
The production of oil and gas can be stimulated by a technique, known as hydraulic (or fluid) fracturing, in which a fluid composition is introduced into an oil or gas well at a flow rate and pressure which create and/or extend a fracture into the oil- or gas-containing formation. The fluid composition usually carries a proppant (e.g., sand, bauxite, etc.) which is forced into the fracture by the fluid composition and prevents closure of the formation after the fluid pressure is released. For example, in my prior patent, described above, I disclosed using my aqueous reaction products in hydraulic fracturing. Earlier examples of fluid fracturing of oil and gas wells involved the use of: aqueous alcoholic solutions of natural gums which had been thickened by the use of inorganic alkali metal or alkaline earth metal salts in U.S. Pat. No. 3,634,237; hydratable polysaccharides cross-linked by TiC1.sub.4 in U.S. Pat. No. 4,033,415; and solvatable polysaccharides cross-linked with ammonium tetralactotitanate(IV) or bis(triethanolamine)bis(isopropyl)titanium in U.S. Pat. No. 3,888,312.
The process and the products of the present invention provide advantages over those of the prior art. The compositions of the present invention are more effective as cross-linkers than those of Russell. Moreover, the products of the present invention are prepared directly from a titanium salt, such as TiC1.sub.4, thus eliminating the step of preparing the titanate commonly used in the prior art. In addition, the process and products of the present invention involve an aqueous medium, thereby avoiding flammmability and pollution problems associated with some of the prior art processes. The compositions of this invention are more effective in cross-linking high molecular weight hydroxyl-containing compositions at high temperatures (150.degree.-300.degree. F.) than are those of the prior art, including those of my prior patent described above. Furthermore, compositions of this invention give cross-linking results which are more reproducible than those of the prior art and which make more effective use of the Ti values. Also the process of this invention takes substantially less time to run than that of my prior patent.